Currently, a new direction of development is to replace amorphous silicon (a-Si) thin film transistors (TFTs) with metal oxide TFTs as the latter have higher mobility. A regular metal oxide TFT may have any of the following three configurations: a back channel protection (ESL) type, a back channel etching (BCE) type, and a common planar (Complar) type. The last two types of metal oxide TFTs have some problems in terms of TFT characteristic and stability, as a result, the ESL type metal oxide TFTs have been widely researched and brought into mass production.
A metal oxide TFT used in an Advanced-Super Dimensional Switching (AD-SDS) technology is generally fabricated through a patterning process with seven masks (7 masks), which successively comprises steps of patterning a gate electrode, patterning an active layer 4, patterning an etch stop layer 5, patterning source and drain electrodes, patterning a first electrode, patterning a planarization layer and patterning a second electrode. To improve the stability of an array substrate, the source and drain electrodes are connected to the active layer 4 respectively through via holes.